Automotive inertia switch with dashpot type actuator

ABSTRACT

Herein disclosed is a mechanical pressure switch device which serves not only as a support mechanism for a bumper of a motor vehicle but as a combination impact detector and switch which is actuated in response to a frontal or rear-end collision encountered by the motor vehicle, comprising in one preferred form a cylinder, a piston axially slidable in the cylinder bore and dividing the cylinder bore into two chambers which are in communication with each other through an orifice formed in the piston, pressure absorptive means such as liquid filling the chambers in the cylinder, and switch means which is actuated in response to the axial movement of the plunger relative to the cylinder through a predetermined distance. The pressure absorptive means may include an incompressible or compressible fluid or an elastic or resilient material in the chamber or chambers in the cylinder. The switch device is connected at one end to the bumper and at the other to a suitable structural member of the vehicle body.

United States Patent Matsui et a1.

[ Feb. 19, 1974 AUTOMOTIVE INERTIA SWITCH WITH 3,593,277 7/1971 Faude ZOO/61.45 R x DASHPOT TYPE ACTUATOR 3,668,337 6/1972 Sinclair n 2,223,097 11/1940 Ehret ZOO/61.45 R UX Inventors: Matsul, Yokohama; 3,562,455 2/1971 McQueen ZOO/81.9 M

Yoshikazu Hayakawa, Yokosuka; jKeuzo Hirashima, Yokohama of Primary Examiner-James R. Scott apan [73] Assignee: Nissan Motor C0mpany, Limited, [57] ABSTRACT Yokohama clty Japan Herein disclosed is a mechanical pressure switch de- [22] Filed: Apr. 27, 1972 vice which serves not only as a support mechanism for a bumper of a motor vehicle but as a combination im- [21] Appl' No.. 248,241 pact detector and switch which is actuated in response to a frontal or rear-end collision encountered by the [30] Foreign Application Priorit D t motor vehicle, comprising in one preferred form a cyl- Apr. 27 1971 Japan 46-32794 ind, Piston axially slidable the cylinder and May 1971 Japan I i t 4640660 dividing the cylinder bore into two chambers which Nov. 6 1971 Japan 46-10370 are in communication with each other through fice formed in the piston, pressure absorptive means [52] CL zoo/61.45 R 200/34 200/6108 such as liquid filling the chambers in the cylinder, and ZOO/615,3 ZOO/8,2 R 335/61 switch means which is actuated in response to the [51] Int. Cl. H01 h 35/02 axial movement of the plunger relative to the cylinder [58] Field of Search. 200/34, 61.08, 61.45 R, 61.53, mmufih predetermined dimm- The Press"re 200/81 9 R 819 M 82 R 86.5. 335/59 61 sorptive means may include an incompressible or v compressible fluid or an elastic or resilient material in [56] References Cited the chamber or chambers in the cylinder. The switch device is connected at one end to the bumper and at UNITED STATES PATENTS the other to a suitable structural member of the vehi- 3,l79,396 4/1965 Bracken 200/34 X 1 body 3,334,204 8/1967 Brenny et a1. 3,551,620 12 1970 Hoover zoo 81.9 M 15 Claims, 13 Drawing Figures 46 4e 7/ I //l/ 4/" A 1 9 v v o 0 p a 0 I A D 34 ,1 /1\\V 1 v 1 H--- x a m 52 Fl :;1 30 1* a 50 Q8 X m f 1 M938 220 26 20o PATENTEDFEB 1 9 1974 SHEET 4 0F 4 AUTOMOTIVE INERTIA SWITCH WITH DASHPOT TYPE ACTUATOR The present invention relates to mechanical pressure responsive switch devices and, more particularly, to switch devices which are adapted to be actuated in response to mechanical pressures applied thereto as a result of compression, deformation or unusual movement of objects which are brought into forceful contact with other moving or stationary objects which may be parts of machines or vehicles. The pressure responsive switch device herein disclosed is especially advantageous where used on motor vehicle safety devices, although such device may find various practical applications in other fields. The present invention, as such, will be herein described, by way of example, as being applied to actuating means for the motor vehicle safety devices which per se are well known in the art.

Various types of motor vehicle safety devices have thus far been proposed for the purpose of providing assurance of safety of the occupants of the motor vehicles in the event of collisions encountered, typical of such safety devices using inflatable protector bags or stretchable protector nettings. The protector bag or netting is usually stowed in a folded or collapsed condition when it is held inoperative. The protector bag or netting is connected to suitable actuating means by which the bag or netting is actuated into a protective position immediately when the collision is encountered by the motor vehicle. The protector bag or netting in this protective position intervenes between the vehicle occupant and relatively hard structural parts of the vehicle cabin such as a wind-shield, an instrument panel, a steering wheel or column, a seat back and so forth. The vehicle occupant violently flung or bounced around by a force of inertia resulting from the collision condition is considerably softly received by the expanded protector bag or the netting which is stretched. The protector bag or netting thus serves as a restraint for the vehicle occupant so as to absorb or dampen out at least a portion of the momentum developed in the occupant as a result of the impact imparted to him. For the purpose of providing full assurance of protection of the vehicle occupant from incurring a serious injury during the collision condition, it is of critical importance that the protector bag or netting be actuated to the protective position as rapidly and reliably as possible and maintained inoperative unless a condition which is likely to lead to a serious danger of the vehicle occupant is brought about. The actuating means for the protector bag or netting is thus required to be responsive to the collision conditionnot only instantaneously but with utmost certainty and is, therefore, usually connected to switch means which is adapted to detect the collision of the motor vehicle upon sensing of either the rate of deceleration of the motor vehicle or the mechanical pressure resulting from the compression, deformation or unusual movement of any of the parts and structures of the motor vehicle as caused by the collision.

The switch means of the type responsive to the rate of deceleration (or acceleration) generally use a magnet and a ball or weight of a'ferromagnetic material serving as an inertial mass and features rapid response to the collision condition. The switch means of this character, however, tends to respond to shocks or impacts of the degrees which are unlikely to invite a serious injury of the vehicle occupant and is, therefore, liable to cause the protector bag or netting to be objectionably actuated when, for instance, the door of the motor vehicle is violently shut or the motor vehicle encounters a hole or depression in the road surface.

The switch means of the mechanical pressure responsive character, on the other hand, respond to an actual collision condition through detection of forceful contact between a part of the vehicle body and an obstruction but are not fully acceptable because of the appreciable delay in actuating the protector bag or netting.

It is, therefore, an object of the present invention to provide a mechanical pressure responsive switch means which is capable of rapidly and reliably detecting the collision condition so as to enable the motor vehicle safety device to be actuated to the protective position at a proper timing and only during a condition in which an impact likely to lead to a serious injury of the vehicle occupant is imparted to the switch means.

The pressure responsive switch device to which the present invention is directed uses a contractable bumper support which is adapted to absorb a force of impact on the bumper by cushioned contraction of a hydrostatic piston cylinder. In accordance with the present invention, the collision of the motor vehicle is detected through use of the forced contraction of the piston cylinder to a predetermined critical extent.

The switch device according to the present invention thus generally comprises a cylinder having a closed end wall, a piston which is axially slidable in the cylinder and which defines at least one chamber in the cylinder between the piston and the closed end wall of the cylinder, a plunger extending axially from the piston in a direction opposite to the closed end wall of the cylinder and projecting outwardly from the cylinder, pressure absorptive means which is accommodated in the cylinder and usually holding the piston and plunger in rest positions, the pressure absorptive means being operable to allow restricted axial movement of the plunger in unison with the piston toward the closed end wall of the cylinder when a mechanical pressure is exerted axially on the plunger, and switch means which is actuated in response to the movement of the plunger and piston through a predetermined distance. Where the cylinder has only one chamber which is defined between the piston and the closed end wall of the cylinder, the pressure absorptive means may comprise a compressible fluid or an elastic or resilient material occupying that chamber. The compressible fluid may be either a gas under pressure or a substantially compressible liquid such as silicon oil while the elastic or resilient material may be rubber, ductile plastics or the like. Where, on the other hand, the cylinder has two chambers which are formed on both sides of the piston, the pressure absorptive means may include compressible or incompressible liquid occupying these two chambers and orifice means providing restricted liquid communication between these chambers. When, thus, the plunger is forced in unison with the piston toward the closed end wall of the cylinder, the liquid in one of the chambers in the cylinder is passed to the other chamber so as to allow the piston and plunger to move accordingly. If, in this condition, the piston and plunger are moved through the predetermined distance, then the switch means is actuated to produce a signal representative of the collision condition. The pressure absorptive means of the above described nature may further include a movable partition member which is axially movable in the chamber defined between the piston and the closed end wall of the cylinder for dividing the chamber into two separate compartments. One compartment which is defined between the movable partition member and the closed end wall of the cylinder is filled with a gas under pressure and the other compartment is filled with the aforesaid liquid and communicates with the opposite chamber in the cylinder through the orifice means. The gas under pressure will add to the cushioning effect for the axial movement of the piston and plunger, absorbing mechanical pressures of a certain magnitude which may be determined by the limit of compression of the gas used.

The switch means which is operable in the switch device thus arranged may be constructed in various manners in accordance with the present invention. For instance, the switch means may comprise a pair of electric contacts which are spaced apart from each other when the plunger and piston are held in the reset positions. These electric contacts are responsive directly or indirectly to the axial movement of the piston in unison with the plunger, thus being brought into contact with each other when the movement of the piston reaches the predetermined distance. In a preferred form of the switch means thus arranged, one of the spaced electric contacts is held stationary relative to the cylinder and the other contact is mounted on the plunger or piston so as to be movable therewith relative to the stationary contact. In this instance, the stationary contact may be positioned at an end of the cylinder opposite to the closed end wall thereof while the movable contact may be mounted on an outer peripheral wall of the plunger at a spacing from and substantially in alignment with the stationary contact so that the two contacts are connected together by the axial movement of the piston and plunger. Alternatively, the stationary contact may be mounted on a contact support member which is held stationary relative to the cylinder and which extends into the plunger through the piston, in which instance the plunger has an axial bore formed therein and receives in the bore the movable contact which is positioned substantially in axial alignment with the stationary contact. In another preferred form of the switch means using the spaced electric contacts, the contacts are supported within an electrically non-conductive receptacle which is mounted on an outer peripheral wall of the plunger at a spacing from the end of the plunger opposite to the closed end wall thereof. The electric contacts are mounted within this receptacle and are spaced apart from each other in an axial direction of the plunger so that they are connected to each other when the plunger is axially moved relative to the cylinder and the receptacle is forced against the end of the cylinder opposite to the closed end wall thereof. As an alternative to the switch means which is thus responsive directly to the axial movement of the plunger and piston relative to the cylinder, the switch means may be arranged so that it is responsive to a rise in the pressure in the liquid or gas contained in the cylinder. The switch means of this nature may comprise a receptacle having a cavity formed therein and a portion constituting the stationary contact, a plug member which is slidable in the cavity in the receptacle and which has a portion constituting the movable contact, and biasing means such as a coil spring urging the plug member outwardly in the receptacle against the pressure of the liquid or gas exerted on the outer face of the plug member so that the stationary and movable contacts are kept spaced apart from each other when the piston and plunger are held in the rest positions in the absence of a pressure on the plunger. When, thus, a mechanical pressure greater than a predetermined magnitude is axially applied to the plunger and consequently the fluid pressure on the plug member increases to a predetermined level, the plug member is caused to slide against the opposing force of the biasing means so that the movable contact integral with the plug member abuts against the stationary contact, thereby producing an electric signal representative of the collision condition detected by the switch device. The switch means thus far described all use two electric contacts which are mechanically connected to response to the movement of the piston and plunger or to the rise in pressure of the liquid or gas in the cylinder. If desired, however, the switch means may be constructed in a manner to produce an electric signal through utilization of an electromotive force induced in a solenoid coil by relative movement of the coil and suitable magnet means. In the switch means of this character, either of the solenoid coil and magnet means is held stationary relative to the cylinder and the other of them is supported on the plunger or piston. The solenoid coil and magnet means are spaced apart from each other when the piston and plunger are held in the rest positions so that no electromotive force is induced in the solenoid coil. When the piston and plunger are moved together through the predetermined distance in response to an impact on the plunger, the solenoid coil and magnet means are aligned with each other so that the solenoid coil cuts at an increasing rate across the magnetic field established by the magnet means. The magnet means may be made up of a pair of permanent magnets which are spaced apart from each other so as to admit therebetween the solenoid coil when the magnets and solenoid coil are aligned together. Alternatively, the magnet means may comprise a permanent magnet of a ring form having a central aperture of a diameter'adapted to admit therein the solenoid coil when the coil and magnet are aligned together. In this instance, the solenoid coil is wound on the plunger and the magnet is supported within the cylinder in a manner to surround the plunger. The plunger and cylinder are formed of a ferromagnetic material and are connected to each other through a ferromagnetic member so as to constitute a magnetic circuit between the magnet and plunger. It is apparent that the permanent magnet or magnets can be substituted by an electromagnet, if desired.

The switch means thus far described are all adapted to be closed so as to produce an ON signal in response to a collision condition thereby detected. If preferred, however, the switch means may be arranged in a manner to open in response to an impact thereon so as to produce an OFF signal during a collision condition. For this purpose, the switch means may comprise a rupturable, electrically conductive element which is constantly energized from a source of electric power and which is ruptured and consequently made nonconductive in response to an impact which is applied thereto. The conductive element of this nature may be a rod or tube of glass which is coated or plated with conductive metal or containing therein a thin wire of conductor.

Where the mechanical responsive switch device is to be used as the collision detecting element of the motor vehicle safety device as previously mentioned; the switch device should be connected at one end to a reverse side Of the bumper and at the other to any of the structural members of the vehicle body, thus extending in its entirety in a fore-and-aft direction of the motor vehicle so as to be responsive to a frontal or rear-end collision of the vehicle.

More detailed constructions and operations of the mechanical pressure responsive switch device according to the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, wherein corresponding parts and materials are denoted by like reference numerals throughout the figures and in which:

FIG. 1 is a longitudinal sectional view of a preferred embodiment of the switch device according to the present invention;

FIG. 2 is a side end view showing, partly in section, another preferred embodiment of the switch device;

FIG. 3 is a fragmentary side end view of still another preferred embodiment of the switch device;

FIG. 4 is a sectional view showing, on an enlarged scale, the switch means forming part of the device illustrated in FIG. 3;

FIG. 5 is also a fragmentary side end view of still another preferred embodiment of the switch device according to the present invention;

FIG. 6 is a sectional view showing, on an enlarged scale, the switch means forming part of the device illustrated in FIG. 5;

FIG. 7 is longitudinal sectional view of still another preferred embodiment of the switch device according to the present invention;

FIG. 8 is a sectional view showing, on an enlarged scale, the switch means forming part of the device illustrated in FIG. 7;

FIG. 9 is also a longitudinal sectional view showing still another preferred embodiment of the switch device according to the present invention;

FIGS. 9A and 9B are cross sectional views taken on line IXIX of FIG. 9, thus showing different magnet arrangements of the switch device illustrated in FIG. 9;

FIG. 10 is a longitudinal sectional view showing a modification of the embodiment illustrated in FIG. 9; and

FIG. 11 is a schematic side elevational view of a motor vehicle which is equipped with the mechanical pressure responsive switch device of any of the constructions shown in the preceding figures.

Reference is now made to FIG. 1 illustrating a first preferred embodiment of the switch device according to the present invention. As illustrated, the switch device has a cylinder having a closed end wall 20a and an axial bore formed therein. A piston 22 is axially slidably received within this cylinder 20, dividing the cylinder bore into two chambers 24 and '26. Communication is provided between the chambers 24 and 26 through an orifice 22a which is formed in the piston 22. A plunger 28 having an axial bore 28a extends axially from the piston 22 and throughout the chamber 24 projecting outwardly of the cylinder 20 through an annular end plug 30. This end plug 30 closes an end of the bore in the cylinder 20 opposite to the end wall 20a, thus hermetically sealing off the chamber 24. The chambers 24 and 26 are filled with liquid 32 which is passable from one of the chambers to the other through the orifice 22a in the piston 22. A contact support member 34 extends axially inwardly from the end wall 20a of the cylinder 28 and projects into the bore 28a in the plunger 28 through the chamber 26, terminating halfway in the bore 28a as illustrated. The end of the plunger 28 facing the end wall 200 of the cylinder 20 is closed by an annular sealing member 6 by which the chamber 26 filled with the liquid 32 is hermetically isolated from the bore 28a in the plunger 28. The contact support member 34 carries on its portion extending in the bore 28a a stationary electric contact 38 through an insulating element 40, the contact 38 thus being held stationary relative to the cylinder 20. The plunger 28, nn the othe hand, carries on its inner peripheral wall an electric contact 42 through an insulating element 44, the contact 42 thus being movable with the plunger 28 relative to the cylinder 20. The stationary and movable contacts 38 and 42, respectively, are located substantially in axial alignment with each other within the bore 28a and, when the plunger 28 is maintained in a rest position as illustrated, the contacts are spaced apart from each other a suitable predetermined distance which is herein indicated by L. The contacts 38 and 42 and the associated insulating members 40 and 44 are herein shown as having annular configurations by way of example but, where desired, they may be modified to have other suitable configurations. The contacts 38 and 42 are connected to leads 46 and 46' of an electric circuit intervening between a source of electric power and actuating means (not shown) of, for instance, a motor vehicle safety device. This actuating means may be a solenoid valve which is usually employed to open a source of a gas under pressure for expanding an inflatable protector bag during a collision condition. Thus, the switch device as a whole is connected at one end to a front or rear bumper and at the other to a structural member of a vehicle body in a suitable manner. In the arrangement shown in FIG. 1, the plunger 28 is connected at its leading end to the bumper 48 through suitable fastening means 50 and the cyliner 20 is connected at its end wall 20a to a bracket 52 which is bolted or welded to any structural member (now shown) of the vehicle body. It is, however, apparent that the directional position of the switch device with respect to the vehicle body can be inverted, if desired, in which instance the plunger 28 is connected to the structural member of the vehicle body and the cylinder 20 is connected to the bumper, though not shown in the drawing.

When, in operation, the motor vehicle having the switch device of the above-described construction encounters a frontal or rear-end collision, then the bumper 50 is forced in the direction of an arrow A so that the plunger 28 and accordingly the piston 22 are urged toward the end wall 20a of the cylinder. This causes the liquid 32 in the chamber 26 to be passed to the other chamber 24 at a restricted rate through the orifice 22a in the piston, thereby allowing the plunger 28 to axially move toward the closed end wall 20a of the cylinder. If, thus, the plunger 28 is moved the distance L, then the contact 42 abuts to the stationary contact 38 srthat the leads 46 and 46' are connected together, completing a closed circuit between the source of power and the actuating means of the safety device. The safety device such as the inflatable protector bag is thereby actuated to the protective position receiving the vehicle occupant who is flung thereto in response to an impact resulting from the collision.

The contacts 38 and 42 and/or the associated insulatin g elements 40 and 44 might objectionably act as stops for the axial movement of the plunger 28 if they are rigidly connected to the support member 34 and plunger 28, respectively. To enable the plunger 28 to entirely retract into the cylinder and accordingly absorb the energy of impact in an adequate proportion during the collision condition, it is preferable to use an adhesive for securing the contacts 38 and 42 to the insulating members 40 and 44 and for securing the insulating elements 40 and 44 to the support member 34 and plunger 28, respectively, whereby the contacts and/or the insulating elements are permitted to be disconnected from the support member and plunger by the movement of the plunger. In this instance, the electric circuit for energizing the actuating means of the safety device should be constructed in such a manner that the actuating means remain energized once the leads 46 and 46' are connected together through the abutment of the electric contacts 38 and 42 to each other. By the use of such circuit arrangement, the actuating means of the safety device is capable of operating in a proper condition even though the contacts 38 and 42 happen to be disconnected from each other after they have once contacted together. Here, it is to be noted that, since the switch device according to the present invention is specifically adapted to respond to a collision with a relatively large magnitude, the contacts 38 and 42 need not be restored to the initial position once the switch device has been actuated.

The liquid 32 usable in the switch device shown in FIG. I maybe a usual hydraulic fluid which is usually incompressible but, where desired, the liquid may be a substantially compressible liquid such as for example silicon oil. Alternatively, a suitable elastic or resilient material such as rubber or ductile plastics may ebe accommodated in the chamber 26 defined between the piston 22 and the closed end wall 20a of the cylinder 20, though not shown. In this instance, the switch device need not use sealing elements such as the end plug 30 and sealing member 36 while the piston 22 need not be formed with the orifice 22a.

The spacing L between the electric contacts 38 and 40 in the initial positions should be selected in consid' eration of the magnitude of the impact at which the safety device shoud be actuated responsive to a collision condition.

FIG. 2 illustrates a modification of the switch device of FIG. 1. This modified switch device is characterized in that the stationary and movable contacts, which are now designated by reference numerals 54 and 56 respectively, are mounted on the outer peripheral wall of the plunger 28 through insulating elements 58 and 60, respectively. The stationary contact 54 is in close contact with the leading end of the cylinder 20 receiving the plunger while the movable contact 56 is positioned on plunger 28 at a spacing L from the stationary contact 54 as seen in the drawing. The stationary and movable contacts 54 and 56 are connected to leads 46 and 46', respectively, of the electric circuit for the actuating means of the safety device. The internal construction of the cylinder 20 may be similar to that of the cylinder of the switch device shown in FIG. 1, except for the fact that the contact support member 34 of the cylinder shown in FIG. I is removed from the cylinder of the device of FIG. 2. It is, however, apparent that the cylinder 20 of the device shown in FIG. 2 may use an elastic or resilient material or a compressible liquid as the pressure absorptive means, as previously mentioned. The plunger 28, on the other hand, may be formed as solid or, if desired, formed with an axial bore communicating with the chamber between the piston and the closed end wall of the cylinder and filled with the liquid or the elastic material.

When, in operation, the plunger 28 of the switch device shown in FIG. 2 is forced toward the bracket 52 in response to an impact resulting from a collision at the bumper 48, then the liquid in the cylinder bore is caused to pass from one of the chambers to the other or the elastic or resilient material is compressed so that the plunger 28 is axially moved in the direction of arrow A. If, thus, the plunger 28 is moved through the distance L which is predetermined, the movable contact 56 is brought into contact with the stationary contact 54 which is, in this condition, disconnected from the plunger 28 and forced against the leading end of the cylinder 20. The leads 46 and 46 are in this manner connected to each other, thereby completing the electric circuit for the actuating means of the safety device. The electric contacts 54 and 56 and/or the insulating elements 58 and 60 should be releasably mounted on the outer peripheral wall of the plunger 28 by use of an adhesive, for the reason previously explained in connection with the switch device shown in FIG. 1. Thus, the electric arrangement for the actuating means for the safety device may be preferably provided with self-holding characteristics though use of a relay or a flip-flop, whereby the actuating means is energized reliably even in the event that the contacts 54 and 56 or the leads 46 and 46 happen to be disconnected from each other once they have been connected together.

The contacts 54 and 56 are shown as generally annular in FIG. 2 but such is by way of example only. If desired, therefore, the contacts 54 and 56 may be formed and located in various other manners.

FIG. 3 illustrates a further modification of the switch device shown in FIG. 2, wherein the spaced electric contacts are integrated into a single unit. The single switch unit, designated by reference numeral 62, is attached to the outer peripheral wall of the plunger 28 and spaced apart from the leading end of the cylinder 20. The detailed internal construction of the cylinder 20 is substantially similar to any of the constructions previously discussed and, as such, no description thereof will be herein incorporated. An example of the construction of the switch unit 62 is illustrated in FIG. 4. As seen in FIG. 4, the switch unit comprises a generally annular receptacle 64 of an insulating material having formed therein an annular cavity (not numbered). A pair of electric contacts 66 and 66' are received within this cavity in the receptacle 64 in a manner to surround the outer peripheral wall of the plunger 28. These contacts 66 and 66' are spaced apart from each other in a direction parallel to the axis of the plunger 28. If desired, annular lands (not numbered) may be formed radially on the inner and outer walls of the receptacle so as to have the contacts 66 and 66' securely separated from each other when the switch unit 62 is maintained inoperative as illustrated. The spacing betwen the contacts 66 and 66 and/or the spacing between the switch unit 62 and the leading end of the cylinder 20 should be selected so that the switch device will be capable of responding to an impact of a predetermined magnitude. The contacts 66 and 66 are connected to leads 46 and 46 of the electric circuit for the actuating means of the safety device, as previously mentioned. During the operation of the switch device in which the bumper 48 is subjected to a collision, the plunger 28 is moved in the direction of arrow A and accordingly the switch unit 62 strikes forcefully against the leading end of the cylinder 20. The receptacle 64 is consequently ruptured or contracted in the axial direction of the plunger 28 with the result that the contacts 66 and 66' are forced against each other. The leads 46 and 46 are thus connected together and as a consequence the safety device is actuated to the protective position by the aid of the actuating means. The annular configuration of the switch unit 62 as shown in FIG. 3 is by way of example and may be modified in any desired manner insofar as such unit is adapted to enable the spaced contacts to bear against each other when it strikes against the cylinder.

FIGS. 5 and 6 illustrate other modifications of the switch device of FIG. 2. Different from the embodiments thus far described wherein the output lead from the switch device is energized only when the collision condition is responded to, the switch device shown in FIG. 5 is so constructed as to be brought into an open position when an impact resulting from the collision is applied to the switch device. Thus, the switch device of this nature comprises a rupturable, electrically conductive means 68 which is positioned on the outer peripheral wall of the plunger 28 and in contact with the leading end of the cylinder and a flange or presser member 70 which is secured on the outer peripheral wall of the plunger 28 and positioned at a spacing from the rupturable conductive means 68. A preferred example of this rupturable conductive means 68 is illustrated in cross section in FIG. 5. The rupturable conductive means 68 as shown-includes a receptacle 68a of a resilient insulating material such as rubber or ductile plastics and a rupturable or frangible conductor element 68b which is embedded in the receptacle 68a. The receptacle 68a and accordingly the conductor element 68b are herein shown as being generally annular, surrounding the outer peripheral wall of the plunger 28. The conductor element 68b may be a thin wire or strip of conductor which is adapted to be broken when subjected to a mechanical pressure greater than a predetermined magnitude or as shown in FIg. 6 a rod or tube of glass which is coated or plated with an electrically conductive metal film. The conductor element 68b in any form is connected at spaced points thereof to the above-mentioned input and output leads 46 and 46' of the electric circuit for the actuating means of the safety device. During a collision condition which is encountered at the bumper 48 of the motor vehicle, the plunger 28 is moved in the .direcdtion of arrow A in the same manner as described previously and, as a consequence, the flange or presser member 70 is forced against the rupturable conductive means 68. The receptacle 68a of the means 68 is accordingly deformed or torn apart so that the conductor element 68b contained therein is cut off or ruptured into fragments, thereby causing the input and output leads 46 and 46 of the electric circuit to be disconnected from each other. It is apparent that'the circuit for the actuating means of the safety device to which the switch device herein shown is applicable should be so arranged as to actuate the safety device when an operating signal produced by interruption of the electric connection between the input and output leads of the switch device is supplied to the actuating means. By preference, the switch devices shown in FIGS. 5 and 6 may be modified in such a manner that the rupturable conductive means 68 is initially spaced apart from the cylinderwhen the plunger 28 is in the rest position so as to be pressed upon by the leading end of the cylinder 20 when the plunger 28 is caused to retract into the cylinder 20. In the construction of this particular nature, the cylinder per se serves as the presser member and, thus, the flange 70 on the plunger 28 may be dispensed with. It is, in this instance, important that the receptacle of the rupturable conductive means be secured to the plunger with sufficient rigidity.

The embodiments thus far described with reference to FIGS. 2 to 6 feature simplicity of construction and ease of production for the simplified constructions and arrangements of the switch means. The construction of the switch unit 62 or the rupturable conductive means 68, moreover, are apparently applicable to the switch device shown in FIG. 1 or 2 through suitable modification incorporated thereinto, where the rupturable conductive means 68 is to be utilized as the switch means of the device according to the present invention, the electric circuit for the actuating means for the safety device need not be provided with self-holding characteristics because the output lead from the switch device remains de-energized FIG. 7 illustrates another embodiment of the switch device according to the present invention which is now constructed as a hydro-pneumatic spring unit using not only the liquid but also a gas under pressure as the pressure absorptive means. Parts and means corresponding to those of the embodiments previously described are designated by like reference numerals. The chamber 26 which is thus defined between the piston 22 and the closed end wall 20a of the cylinder 20 is now divided into two compartments 26a and 26b by means of a movable partition member 72 serving as a floating piston. The partition member 72 is axially slidable in the chamber 26 through a sealing member 74 closely received between the peripheral edge of the partition member 72 and the inner peripheral wall of the cylinder for hermetically sealing off the compartments 26a and 26b. The compartment 26a defined between the piston 22 and the partition member 72 is filled with liquid 32 and communicates with the chamber 24 through the orifice 22a in the piston 22. The other compartment 2612 which is defined between the partition member 72 and the closed end wall 20a of the cylinder 20 is occupied with a gas 76 under pressure. When, thus, the plunger 28 and piston 22 are held in the rest positions in the absence of an impact on the bumper 48, the movable partition member 72 is maintained in a balanced position in which equalized liquid and gas pressures are exerted on both sides thereof. The switch means which is applicable to the switch device thus constructed may be of a construction which is similar to any of the constructions of the switch means previously described wherein the switch means is actuated in direct response to the axial movement of the plunger relative to the cylinder during the collision condition. If preferred, however, the switch means may be arranged in a manner to be responsive to a rise in the pressure in either the liquid 32 in the compartment 26a or the gas 76 in the compartment 26b of the cylinder 20, an example of the switch means thus constructed being illustrated in Flg. 8. Referring to FIG. 8, the switch means designated by reference numeral 78 includes a receptacle 80 of a substantially rigid, electrically conductive material having a cavity 82 formed therein. This receptacle 80 is opened at one end and closed at the other by an end wall 80a. A projection 84 is formed on the end wall 80a, extending through the cavity 82 toward the open end of the receptacle 80, as shown. This projection 84, formed of the electrically conductive material, serves as a stationary contact. A plug member 86 is slidably received in the cavity 82 in the receptacle through a sealing member 88 interposed between the'plug member 86 and the inner peripheral wall of the receptacle 80. The plug member 86 has formed on its inner peripheral face a land or projection 90 which is in line with the projection 84 from the end wall 80a of the receptacle. The plug member 86 and the land 90 forming part thereof are formed of a substantially rigid, electrically conductive material so that the land 90 serves as a movable contact which is engageable with the stationary contact constituted by the projection from the end wall 800 of the receptacle 80. A preload or compression spring 92 is mounted within the cavity 82 in the receptacle 80 in a manner to surround the projection 84 of the end wall 80a and the land 90 of the plug member 86. This compression spring 92 is seated at one end on the inner face of the end wall 800 through a spring seat 94 and an insulating element 96 and at the other on the inner face of the plug member 86 through a spring seat 98 and an insulating element 100. The compression spring 92 biases the plug member 86 outwardly, viz., away from the end wall 80a of the receptacle 80, thereby keeping the land or movable contact 90 on the plug member 86 spaced apart from the projection or stationary contact 84. The receptacle 80 and plug member 86 are electrically isolated from each other by means of an insulating element 102 which is attached to the inner peripheral wall of the receptacle. The receptacle 80 and plug member 86 are respectively connected to leads 46 and 46' of the electric circuit for the actuating means of the safety device. The projection 84 and land 90 serving as the stationary and movable contacts, respectively, in the shown construction are formed integrally with the receptacle 80 and plug member 86, respectively. Where, however, it is desired that the receptacle 80 and plug member 86 be formed with an insulating material of materials, the stationary and movable contacts may be constituted by electrically conductive members which are connected to the end wall 80a of the receptacle 80 and the plug member 86 and which are configured generally in correspondence with the projection 84 and land 90. In this instance, the conductive members corresponding to the projection 84 and lead 90 should be directly connected to the leads 46 and 46' of the electric circuit for the safety device actuating means while the insulating elements 96, 100 and 102 need not be used.

The switch means 78 having the above described construction is mounted on the cylinder of the switch device in a manner to have its plug member 86 kept in contact with either the liquid 32 in the compartment 26a or the pressurized gas 76 inthecompartment 26b, as seen in FIG. 7. Thus, the plug member 86 is usually held in a balanced position through equilibrium between the biasing force of the compression spring 92 and the opposing liquid or gas pressure exerted on the outer face of the plug member 86. In the absence of an increased pressure in the liquid 32 or the gas 76 with the plunger 28 and accordingly the piston 22 held in the rest positions, the land or movable contact 90 is kept disconnected from the projection or stationary contact 84 so that the safety device actuating means is held inoperative.

When, now, the bumper 48 is forced toward the cylinder 20 as a result of a collision, the plunger 28 and piston 22 are urged toward the end wall 200 of the cylinder in the direction of arrow A with the result that the liquid 32 in the compartment 26a is subjected to a pressure This pressure on the liquid 32 is dampened partially by passage of the liquid to the chamber 24 through the orifice 22a in the piston and partially by compression of the pressurized gas 76 in the compartment 26b. If, in this condition, the pressure transferred to the plug member 86 either from the liquid 32 in the compartment 26a or by the pressurized gas 76 in the compartment 26b reaches a level overcoming the biasing force. of the compression spring, then the plug member 86 is moved toward the end wall a of the re ceptacle 80 until the land or movable contact abuts against the projection or stationary contact 84. The leads connected to the receptacle 80 and plug member 86 (or directly to the stationary and movable contacts mounted in the receptacle and plug member when formed of the insulating material) are interconnected so that the electric circuit for the actuating means of the safety device is energized and accordingly the safety device is actuated to the protective position.

FIG. 9 illustrates still another embodiment of the switch device in accordance with the present invention, wherein the electric signal indicative of the collision condition of the motor vehicle is produced by means of an electromotive force which is induced as a result of the movement of the plunger relative to the cylinder. The cylinder and piston arrangements of the switch device shown in FIG. 9 are exemplified as being essentially similar to those of the device illustrated in FIG. 7 and, therefore, corresponding parts and elements are designated by like reference numerals. It is, however, apparent that the cylinder and piston arrangements of the device herein shown can be of a nature substantially corresponding to any of the cylinder and piston arrangements shown in FIGS. 1 and 2 or the modifications thereof. The switch device shown in FIG. 9 now includes a solenoid coil 104 which is wound on the outer peripheral wall of the leading end portion of the plunger 28 and which is suitably spaced apart from the leading end of the cylinder 20. This solenoid coil 104 is connected at its ends to the leads 46 and 46' of the electric circuit for the safety device actuating means. A pair of permanent magnets 106 and 106are attached to the leading end wall of the cylinder 20 and substantially diametrically opposed to each other across the plunger 28 extending therebetween, as better seen in FIG. 9A. These permanent magnets 106 and 106 are supported within a sleeve 108 which is fast on the outer peripheral wall of the cylinder 20. Thus, the magnets 106 and 106' are secured in position between the spaced end walls of the cylinder 20 and sleeve 108 and are axially spaced apart from the solenoid coil 104 when the plunger 28 is held in the rest position illustrated in FIG. 9. If desired, a tubular or otherwise shaped guide member 110 may be axially slidably received on the outer peripheral wall of the sleeve 108. This guide member 110 is usually connected at its end opposite to the cylinder to a bracket 112 through which the plunger 28 is rigidly connected to the bumper or a structural member (not shown) of the vehicle body.

The permanent magnets 106 and 106' establish a magnetic field across the plunger 28. When, thus, the plunger 28 is moved in unison with the guide member 110 toward the closed end wall 20a of the cylinder 20 by a force of impact applied to the bracket 112 through the bumper, the solenoid coil 104 and permanent magnets 106 and 106' approach each other. When the plunger 28 is completely retracted into the sleeve 108, then the solenoid coil 104 is brought into alignment with the magnets 106 and 106' and thus cuts acrossthe magnetic flux at an increasing rate. An electromotive force is consequently induced in the solenoid coil 104 and the leads connected to the electric circuit for the safety device actuating means are energized.

In order to provide for ease of assembly of the switch device of the nature above described, a single permanent magnet 114 of a ring form may be substituted for the co-operating magnets 106 and 106', as seen in FIG. 9B. In this instance, the sleeve 108, guide member 110, bracket 112 and plunger 28 should be made of a ferromagnetic material or materials so that the sleeve 108 and plunger 28 serve as pole pieces having opposite polarities. Thus, an annular air gap is formed between the plunger 28 and the permanent magnet l 14, establishing a magnetic field therein. The operation of the switch device above described is entirely the same as that of the device having the construction shown in FIG. 9A.

A modified embodiment of the switch device shown in FIG. 9 is now illustrated in FIG. 10. The switch device herein shown uses a plunger 116 having an axial bore (not numbered) which is in constant communication with the axial bore in the cylinder 20 which is,

closed at the end wall 20a. The bored plunger 116 supports an apertured piston 118 at its end facing the closed end wall 20a of the cylinder 20 and is axially slidable together with the piston 118 in the bore in the cylinder 22 toward the end wall 20a. The piston 118 thus defines a chamber 120 between the piston and the closed end wall 20a of the cylinder and a chamber 122 defined between the piston and an end plug 124 mounted at the end of the plunger 116 opposite to the piston l 18. The piston 118 is formed with a central aperture 118a of a predetermined diameter through which constant communication is provided between the chambers 120 and 122. The chamber 122 is divided into two compartments 122a and 122b by a movable partition member 126 which is axially slidable in the chamber 122. The chamber 120 and accordingly the compartment 122a defined between the piston 1 18 and partition member 126 are filled with liquid 128 while the compartment 122b defined between the partition member 126 and end plug 124 is filled with a gas 130 under pressure. A liquid flow restricting rod 132 projects from an inner face of the closed end wall 20a of the cylinder 20 and extends into the liquid compartment 122a of the plunger through the central aperture 118a in the piston l 18, thereby forming an annular orifice (not numbered) between the piston 118 and rod 132. This flow restricting rod 132 is usually tapered toward its leading end so as to provide a gradually increasing restriction of the flow of the liquid through the annular orifice when the plunger 116 is axially moved relatively toward the end wall 20a of the cylinder 20. The rod 132 carries a solenoid coil 134 at its portion located within the liquid chamber while the apertured piston 118 has embedded therein a pair of magnets 136 and 136' which are generally diametrically opposed to each other. Similarly to the arrangement shown in FIG. 9B, a single permanent magnet of a ring form may be used in lieu of the magnets 136 and 136' in the device shown in FIG. 10 though not illustrated in the drawing. The magnets 136 and 136 are thus spaced apart from the solenoid coil 134 when the plunger 116 and accordingly the piston 118 are held in the rest positions in the absence of an impact on the plunger so that the solenoid coil 134 remains deenergized so as to hold the safety device inoperative. The solenoid coil 134 is at both ends connected to the leads 46 and 46 of the electric circuit of the safety device actuating means. When, however, an impact is applied to the plunger 116 through the end plug 124 which is usually rigidly connected to the bumper or structural part of the vehicle body, then the plunger 1 16 is axially moved toward the end wall 20a of the cylinder with the gas in the compartment 1221) compressed and with the liquid 128 in the chamber 120 displaced into the liquid compartment 122a. This causes the piston 118 and accordingly the magnets 136 and 136' to be brought into alignment with the solenoid coil 134 on the rod 132 with the result that an electromotive force is induced in the solenoid coil 134. The solenoid coil 134 is consequently energized so that the actuating means connected thereto is initiated into action to actuate the safety device into the protective position.

The positional relationship between the solenoid coil and permanent magnet or magnets as shown in FIG. 9 or 10 may be reversed, if desired. In this instance, the switch device shown in FIG. 9 may be modified so that the solenoid coil 104 is supported on the sleeve I08 and the magnets 106 and 106' on the plunger 28 while the switch device shown in FIG. 10 may be modified so that the solenoid coil 134 is mounted on the apertured piston 118 and the magnets 136 and 136' on the flow restricting rod 132. It is apparent that the particular construction of the switch means using the combination magnet and coil as illustrated in FIG. 9 or 10 is also applicable to the arrangement of the hydrostatic unit shown in FIG. 1 or 2 or to the arrangements using the elastic or resilient material as the pressure absorptive means provided suitable modification is made in the prototype arrangements. The permanent magnet or magnets forming part of the switch device shown in FIG. 9 or 10 may be replaced with an electromagnet where desired.

Where the switch device of any of the constructions thus far described is to be mounted on the motor vehicle, the device may be positioned and located in any desired manner depending upon the operation requirements of the safety device. In view, however, of the fact that the collisions are encountered by the motor vehicles usually at the front or rear bumpers with few exceptions and that the motor vehicle safety devices are most useful in the event of the frontal or rear-end collisions, it is most preferable that the switch device according to the present invention be mounted in association with the front or rear bumper of the motor vehicle as seen in FIG. 11. In FIG. 11, the switch device according to the present invention as indicated by S, at the front or by S at the rear of the motor vehicle is shown as mounted between the front or rear bumper B or B respectively, and the structural member (not numbered) of the vehicle body.

It may be noted that, although the switch devices and accordingly the various component parts and elements of the switch devices have been described and shown as having generally circular cross sections, such is merely by way of example. Thus, the switch device of any construction herein disclosed and the component parts thereof may have any desired cross sections insofar as they are acceptable from the view point of production efficiency and economy and the performance quality of the resultant switch device.

lt will now be appreciated from the foregoing description that the mechanical pressure responsive switch device according to the present invention is especially useful for use with the safety devices of any kind of the motor vehicles because such device is capable of rapidly and reliably responding to the collision condition which is most likely to be encountered at the front or rear bumpers of the motor vehicles. If desired, the switch device of the nature herein disclosed may be used in combination with switch element or elements of any other character such as the known deceleration or acceleration responsive switch device so as to further enhance the reliability in the detection of the collision condition of the motor vehicle. It should be, however, borne in mind that the applications of the switch device according to the present invention are not limited to the motor vehicle safety devices and, as such, the switch device will prove useful for various other purposes.

What is claimed is:

1. A switch device responsive to impact forces, comprising:

a cylinder closed at one end by an end wall and having an annular plug at the opposite end;

a piston slidable in said cylinder to divide the cylinder bore into a first compartment adjacent said end plug and a second compartment adjacent said end wall;

a plunger fixed to said piston and extending through said second compartment and slidably mounted in said annular end plug and terminating at the exterior of said cylinder;

a liquid filling said first and second compartments;

orifice means in said piston for regulating the flow of liquid from said first compartment to said second compartment to regulate the speed at which said plunger may be moved inwardly into the cylinder bore when subjected to impact forces; and

a switch means responsive to a predetermined inward movement of said plunger into said cylinder by impact forces thereon.

2. A switch device as claimed in claim 1, wherein said switch means comprises:

a first electrical contact mounted on the exterior portion of said plunger adjacent to and exteriorly of the end of said cylinder opposed to said end wall and substantially stationary with respect to said cylinder; and

a second electrical contact attached to the exterior portion of said plunger and spaced axially away from the end of said cylinder opposed to said end wall and substantially in axial alignment with said first contact for contact therewith when said plunger is subjected to impact forces.

3. A switch device as claimed in claim 1, wherein said plunger has an axial cavity closed at the end adjacent to said piston by an annular sealing member, said switch device further comprising a contact support member in the form of a rod extending axially from said end wall through said first compartment and said annular sealing member a first electrical contact attached to the leading end portion of said rod adjacent to said annular sealing member within said cavity and a second electrical contact attached to the inner wall of said cavity in said plunger and normally spaced axially apart from said first contact and said annular sealing memher.

4. A switch device as claimed in claim 1, wherein said switch means comprises an annular electrically insulative deformable member surrounding the outer periphsaid rupturable electrically conductive means being securely mounted on an outwardly projecting portion of said plunger for being ruptured against the opposite end of said cylinder when said plunger is moved inwardly into said cylinder through a predetermined distance by impact forces.

6. A switch device as claimed in claim 5, wherein said rupturable electrically conductive means includes a rupturable piece of glass coated with an electrically conductive film.

7. A switch device as claimed in claim 1, wherein said switch means comprises arupturable, electrically conductive meanswhich is rupturable when subjected to impact forces greater than a predetermined magnitude, a presser member mounted on the outer periphery of an outwardly projecting portion of said plunger, said rupturable, electrically conductive means being mounted at the end of said cylinder opposed to said end wall and normally spaced from and substantially in axial alignment with said presser member for being struck and ruptured by said presser member when said plunger is moved inwardly by impact forces into said cylinder toward the closed end wall thereof through a predetermined distance.

8. A switch device as claimed in claim 1, wherein said switch means comprises a receptacle having a cavity formed therein and mounted in the wall of said first compartment of said cylinder, a plug member slidable in said cavity in the receptacle and having an outer face in contact with said liquid in said first compartment, said receptacle and said plug member having electric contacts on their inner facing walls, and biasing means urging said plug member outwardly from said receptacle against the pressure of said liquid acting on the outer face of said plug member for biasing said electric contacts away from each other, said plug member being moved against the force of said biasing means for allowing said electric contacts to be forced against each other when said liquid is subjected to a pressure in response to the axial movement of said plunger by impact forces toward said closed end wall of said cylinder through a predetermined distance.

9. A switch device as claimed in claim 8, wherein said receptacle and said plug member are formed of an electrically conductive material and in which said electric contacts are formed integrally with said receptacle and said plug member and are aligned with each other within said cavity of said receptacle and further comprising means for electrically insulating said receptacle and said plug means from each other when in-the normal inoperative position.

10. A switch device as claimed in claim 11, and further comprising a free piston sealingly slidable within the first compartment of said cylinder to define a third compartment cooperating with said closed end wall; and a compressible gas filling said third compartment.

11. A switch device as claimed in claim 10, wherein said switch means comprises a receptacle having a cavity formed therein and mounted in the wall of said third compartment of said cylinder, a plug member slidable in said cavity in said receptacle and having an outer face in contact with the gas in said third compartment, said receptacle and said plug member having electric contacts on their inner facing walls, and biasing means urging said plug member outwardly from said receptacle against the pressure of the gas acting on the outer face of said plug member for biasing said electric contacts away from each other, said plug member being moved against the force of said biasing means for allowing said electric contacts to be forced against each other when said gas is subjected to a pressure in response to the axial movement of said plunger by impact forces toward said closed end wall of said cylinder through a predetermined distance.

12. A switch device as claimed in claim 11, wherein said receptacle and said plug member are formed of an electrically conductive material and in which said electric contacts are formed integrally with said receptacle and said plug member and are aligned with each other within said cavity of said receptacle and further comprising means for electrically insulating said receptacle and said plug from each other when in the normal inoperative position.

13. A switch device as claimed in claim 10, wherein said switch means comprises a magnet attached to the end of said cylinder opposed to said end wall to surround said plunger; and a solenoid coil attached to the exterior of said plunger in substantial axial alignment with said magnet and axially spaced apart from the end of said cylinder.

14. A switch device as claimed in claim 1, wherein said cylinder includes a tapered rod secured to the end wall of said cylinder and extending axially within said cylinder through said piston, and said switch means comprises a magnet mounted on said piston and a solenoid coil wound on said rod within said first compartment and normally spaced axially from said piston.

15. A switch device as claimed in claim 14, wherein said orifice regulating means comprises an aperture in said piston through which said tapered rod extends in spaced relation, said tapered rod and said aperture forming the flow regulating orifice. 

1. A switch device responsive to impact forces, comprising: a cylinder closed at one end by an end wall and having an annular plug at the opposite end; a piston slidable in said cylinder to divide the cylinder bore into a first compartment adjacent said end plug and a second compartment adjacent said end wall; a plunger fixed to said piston and extending through said second compartment and slidably mounted in said annular end plug and terminating at the exterior of said cylinder; a liquid filling said first and second compartments; orifice means in said piston for regulating the flow of liquid from said first compartment to said second compartment to regulate the speed at which said plunger may be moved inwardly into the cylinder bore when subjected to impact forces; and a switch means responsive to a predetermined inward movement of said plunger into said cylinder by impact forces thereon.
 2. A switch device as claimed in claim 1, wherein said switch means comprises: a first electrical contact mounted on the exterior portion of said plunger adjacent to and exteriorly of the end of said cylinder opposed to said end wall and substantially stationary with respect to said cylinder; and a second electrical contact attached to the exterior portion of said plunger and spaced axially away from the end of said cylinder opposed to said end wall and substantially in axial alignment with said first contact for contact therewith when said plunger is subjected to impact forces.
 3. A switch device as claimed in claim 1, wherein said plunger has an axial cavity closed at the end adjacent to said piston by an annular sealing member, said switch device further comprising a contact support member in the form of a rod extending axially from said end wall through said first compartment and said annular sealing member a first electrical contact attached to the leading end portion of said rod adjacent to said annular sealing member within said cavity and a second electrical contact attached to the inner wall of said cavity in said plunger and normally spaced axially apart from said first contact and said annular sealing member.
 4. A switch device as claimed in claim 1, wherein said switch means comprises an annular electrically insulative deformable member surrounding the outer peripheral wall of the exterior portion of said plunger and spaced apart from the end of said cylinder opposed to said end wall, said annular material having a cavity therein, two electrical contacts disposed within said cavity normally spaced axially apart from each other with respect to the axis of said plunger.
 5. A switch device as claimed in claim 1, wherein said switch means comprises a rupturable, electrically conductive means which is rupturable when subjected to impact forces greater than a predetermined magnitude, said rupturable electrically conductive means being securely mounted on an outwardly projecting portion of said plunger for being ruptured against the opposite end of said cylinder when said plunger is moved inwardly into said cylinder through a predetermined distance by impact forces.
 6. A switch device as claimed in claim 5, wherein said rupturable electrically conductive means includes a rupturable piece of glass coated with an electrically conductive film.
 7. A switch device as claimed in claim 1, wherein said switch means comprises a rupturable, electrically conductive means which is rupturable when subjected to impact forces greater than a predetermined magnitude, a presser member mounted on the outer periphery of an outwardly projecting portion of said plunger, said rupturable, electrically conductive means being mounted at the end of said cylinder opposed to said end wall and normally spaced from and substantially in axial alignment with said presser member for being struck and ruptured by said presser member when said plunger is moved inwardly by impact forces into said cylinder toward the closed end wall thereof through a predetermined distance.
 8. A switch device as claimed in claim 1, wherein said switch means comprises a receptacle having a cavity formed therein and mounted in the wall of said first compartment of said cylinder, a plug member slidable in said cavity in the receptacle and having an outer face in contact with said liquid in said first compartment, said receptacle and said plug member having electric contacts on their inner facing walls, and biasing means urging said plug member outwardly from said receptacle against the pressure of said liquid acting on the outer face of said plug member for biasing said electric contacts away from each other, said plug member being moved against the force of said biasing means for allowing said electric contacts to be forced against each other when said liquid is subjected to a pressure in response to the axial movement of said plunger by impact forces toward said closed end wall of said cylinder through a predetermined distance.
 9. A switch device as claimed in claim 8, wherein said receptacle and said plug member are formed of an electrically conductive material and in which said electric contacts are formed integrally with said receptacle and said plug member and are aligned with each other within said cavity of said receptacle and further comprising means for electrically insulating said receptacle and said plug means from each other when in the normal inoperative position.
 10. A switch device as claimed in claim 11, and further comprising a free piston sealingly slidable within the first compartment of said cylinder to define a third compartment cooperating with said closed end wall; and a compressible gas filling said third compartment.
 11. A switch device as claimed in claim 10, wherein said switch means comprises a receptacle having a cavity formed therein and mounted in the wall of said third compartment of said cylinder, a plug member slidable in said cavity in said receptacle and having an outer face in contact with the gas in said third compartment, said receptacle and said plug member having electric contacts on their inner facing walls, and biasing means urging said plug member outwardly from said receptacle against the pressure of the gas acting on the outer face of said plug member for biasing said electric contacts away from each other, said plug member being moved against the force of Said biasing means for allowing said electric contacts to be forced against each other when said gas is subjected to a pressure in response to the axial movement of said plunger by impact forces toward said closed end wall of said cylinder through a predetermined distance.
 12. A switch device as claimed in claim 11, wherein said receptacle and said plug member are formed of an electrically conductive material and in which said electric contacts are formed integrally with said receptacle and said plug member and are aligned with each other within said cavity of said receptacle and further comprising means for electrically insulating said receptacle and said plug from each other when in the normal inoperative position.
 13. A switch device as claimed in claim 10, wherein said switch means comprises a magnet attached to the end of said cylinder opposed to said end wall to surround said plunger; and a solenoid coil attached to the exterior of said plunger in substantial axial alignment with said magnet and axially spaced apart from the end of said cylinder.
 14. A switch device as claimed in claim 1, wherein said cylinder includes a tapered rod secured to the end wall of said cylinder and extending axially within said cylinder through said piston, and said switch means comprises a magnet mounted on said piston and a solenoid coil wound on said rod within said first compartment and normally spaced axially from said piston.
 15. A switch device as claimed in claim 14, wherein said orifice regulating means comprises an aperture in said piston through which said tapered rod extends in spaced relation, said tapered rod and said aperture forming the flow regulating orifice. 